1. Field of the Invention
The present invention relates generally to a parallel axes type automatic transmission, and more particularly to a shaft arrangement structure in a parallel axes type automatic transmission.
2. Description of the Related Art
A parallel axes type automatic transmission is configured so that a plurality of input shafts are arranged in parallel to an output shaft and that shift gears (drive gears) rotatably mounted on the input shafts are selectively coupled by wet multiplate clutches to transmit the rotation of the input shafts to the output shaft. The number of wet multiplate clutches is the same as that of shift gears. For example, a parallel axes type automatic transmission having three input shafts and one output shaft is known. This automatic transmission has such a configuration that two wet multiplate clutches for fourth-speed and fifth-speed gears are provided on the first input shaft, two wet multiplate clutches for first-speed and second-speed gears are provided on the second input shaft, one wet multiplate clutch for a third-speed gear is provided on the third input shaft, and the output shaft has no wet multiplate clutch. In this parallel axes type automatic transmission, the second input shaft is arranged at the highest level, and the third input shaft is arranged at the lowest level.
However, the conventional parallel axes type automatic transmission mentioned above has a problem such that the automatic transmission cannot be sufficiently reduced in size because of limiting conditions including the feasibility of mating surfaces of the automatic transmission and an engine and a mounting space for the automatic transmission on a vehicle. Further, splashes of a lubricating oil from the wet multiplate clutches mounted on the input shafts are scattered onto the inner wall of a transmission case, causing the occurrence of aeration and an increase in friction.